The present invention relates to a power switching mechanism for use in robotic applications and, more specifically, for selectively connecting a robotic system to a robot tool.
Many different types and forms of gripping mechanisms are known, providing a variety of functions and uses. Some gripping mechanisms are designed for specific tasks, they are simple, robust, easy to manufacture and lead to simple control schemes. However, they are not flexible and a new gripping mechanism must be designed for each given task. These gripping mechanisms have only a few degrees of freedom and are widely used in industry. Other gripping mechanisms are more flexible and can perform several different tasks. However, they are difficult to manufacture, lead to complex control schemes, include several actuators and can provide only small gripping forces. These gripping mechanisms have several degrees of freedom.
Finally, other gripping mechanisms have an architecture which combines the latter two cases, taking advantage of both through the concept of underactuation. Their design is based on a large number of degrees of freedom but with a reduced number of actuators. Indeed, underactuated gripping mechanisms are defined as those which have fewer actuators than the degree of freedom. This leads to flexible gripping mechanisms without the complexity associated with a large number of actuators.
Underactuation can be achieved using different structural mechanisms. A typical example is described in the Applicants"" U.S. Pat. No. 5,762,390, issued on Jun. 9, 1998. A mechanical gripper, described in this patent, has three fingers and three phalanges per finger. The three pivotable phalanges are actuated by one actuator in a flexible and versatile gripping action of three degrees of freedom. The fingers are robust and can provide large gripping forces and perform power grasps and pinch grasps. An additional mechanism is provided to maintain the last phalanx orthogonal to the palm in order to allow the gripper to perform pinch grasps on objects of different sizes. The mechanical gripper including the limited number of actuators permits the fingers to bend independently so that, by actuating some of the actuators and not actuating others, different co-operative bending relationships are achieved.
In addition to the underactuation between the phalanges of a finger, it is also possible to obtain underactuation between the fingers of a gripping mechanism. This will further decrease the number of actuators while maintaining the same number of degree of freedom. This principle has been disclosed for the actuation of many fingers, for example, in U.S. Pat. No. 5,378,033 to Guo et al. and in the literature, see, for example, the article by G. Guo, X. Qian and W. A. Gruver, xe2x80x9cA SINGLE-DOF MULTI-FUNCTION PROSTHETIC HAND MECHANISM WITH AN AUTOMATICALLY VARIABLE SPEED TRANSMISSIONxe2x80x9d, published in the proceedings of the ASME mechanism conference, Phoenix, Vol. DE-45, pp. 149-154, 1992, and the article by M. Rakik entitled xe2x80x9cMULTI-FINGERED ROBOT HAND WITH SELF-ADAPTABILITYxe2x80x9d, published in Robotics and Computer-Integrated Manufacturing, Vol. 5, No.2-3, pp. 269-276, 1989. In these references, each of the fingers has only one degree of freedom, i.e., the motion of the phalanges is coupled. The combination of the underactuation of the phalanges of a finger and the fingers of a hand is disclosed in the Applicant""s United States Patent. The underactuation between the fingers is performed with the help of a one-input/multi-output differential. The concept of this differential has been introduced in the Applicant""s United States Patent using a lever for two outputs.
It is also possible to orient the fingers with respect to one another (i.e., motion about an axis perpendicular to the palm of the gripping mechanism) with only one actuator by coupling their orientation. This is possible through the use of four-bar mechanisms that connect the base of the fingers. This decreases the number of degrees of the actuation and freedom of the system. This type of coupling has already been suggested in the Applicant""s United States Patent and is provided by gears in U.S. Pat. No. 3,901,547 to Skinner II, and by grooves in the Guo et al. patent.
In order to achieve this underactuation between the fingers in a differential gripping mechanism, the force of the actuator is to be distributed between the fingers. If a finger grasps an object, the actuator will continue its motion and the other fingers will continue to close with the help of the differential mechanism. Nevertheless, this principle associated with a differential mechanism sometimes limits the performance of the gripping mechanism especially in pinch grasps. It may be desirable, for example, to use only two fingers to perform a pinch grasp and prevent the remainder of the fingers from closing which may potentially disturb the grasp. This is not a problem with a gripping mechanism having multiple actuators because each finger is controllably actuated independently.
Therefore, there exists a need for improved gripping mechanisms which are underactuated between fingers using differential mechanisms and adapted to deactivate predetermined fingers in a closing action when it is desired.
It is also desirable to self-lock the fingers when a gripping mechanism grasps an object. It is especially important when a differential mechanism is used for underactuation between the fingers. An external force acting on one of the fingers may cause a displacement not only of the finger receiving the force but also of the remainder of the fingers because all the fingers are associated with the differential mechanism. A lever differential mechanism as described in the prior art is not able to provide the finger self-locking function. Therefore, there exists a need for an actuation system for gripping mechanisms underactuated between fingers, which provides a finger self-locking function.
It is an object of the present invention to provide a power switching mechanism for connecting a robot system having plural degrees of freedom to a robot tool having plural actuators.
Therefore, in accordance with the present invention, there is provided a power switching mechanism for selectively connecting a robotic system having a two-degrees-of-freedom power input to a robot tool having a plurality of actuators, with said two-degrees-of-freedom power input comprising a translation power input and a power shaft rotation input, said switching mechanism comprising:
an axially displaceable connector mounted to said power shaft rotation input for rotating therewith;
an indexing mechanism connected to said power shaft rotation input and axially movable sequentially between a neutral position and an actuator engaging position for each said actuator;
wherein the axially displaceable connector engages any one of said actuators in response to movement of the axial translation of the two-degree of freedom power input.